Calcium imaging experiments were performed as previously described (Deering-Rice et al., 2012 (link); Deering-Rice et al., 2011 (link); Shapiro et al., 2013 (link)). Briefly, cells were loaded with Fluo-4 AM using the Fluo-4 Direct Kit (Invitrogen) diluted in LHC-9 (HEK-293 cells) or calcium assay buffer (HaCaT cells) for 60 min at 37°C (HEK-293) or room temperature (HaCaT). The loading solution was removed and the cells were subsequently incubated 30 min at 37°C (HEK-293) or room temperature (~23°C) (HaCaT) in the dark with LHC-9 (HEK-293) or calcium buffer (HaCaT) containing 0.5 mM probenecid and 0.75 mM trypan red (ATT Bioquest). Treatment solutions were prepared in LHC-9 (HEK-293) or calcium assay buffer (HaCaT) at 3X concentration and 10 or 25 μl was added to 20 or /50 μl of media on the cells in 384- or 96-well plates. Calcium flux responses were measured using either a NOVOstar plate reader (BMG LABTECH, Offenberg, Germany) or microscopically, as previously described in the references above. Where specified, data were corrected for non-specific responses observed with HEK-293 cells, and normalization to the maximum attainable change in fluorescence elicited by ionomycin (10 μM).